The artificial distribution of water onto plants through irrigation systems is in wide use throughout the world today. Many irrigation systems are installed for watering lawns, shrubs, golf courses, and athletic fields. The typical irrigation system for such applications includes a programmable electronic irrigation controller that turns a plurality of solenoid actuated valves ON and OFF in accordance with a watering schedule. The valves deliver water through subterranean pipes to a plurality of sprinklers spaced around the irrigation site. One of the most popular sprinklers currently in use for watering golf courses and athletic fields is the pop-up rotor-type sprinkler. This sprinkler includes a vertically telescoping cylindrical riser that is normally in a retracted position within an outer cylindrical case whose flanged upper end is flush with the surface of the ground. The riser is surrounded by a coil spring that holds the riser in its lowered position within the outer case. When the water to the sprinkler is turned ON, the riser telescopes to its raised position. The riser contains a turbine that drives a nozzle turret through a gear train reduction. The riser also usually contains a reversing mechanism that is manually adjustable to set the arc of oscillation of the nozzle turret. Some rotor-type sprinklers can be set to a full circle rotation mode. Large rotor-type sprinklers sometimes include an ON/OFF valve in the lower portion of the outer case. These sprinklers are referred to as valve-in-head sprinklers.
Rotor-type sprinklers that are used on golf courses and playing fields often eject a stream of water seventy feet or more. These sprinklers sometimes operate at water pressures above one-hundred pounds per square inch. They are subjected to extreme forces over their lifetime of use which can damage them and reduce their useful life. The most serious of these forces results from water hammer and high pressure surges that occur during system winterization and spring recharge. Winterizing involves blowing high pressure air through the pipes to remove the water to prevent damage to the sprinklers from water freezing in the sprinklers. In the spring, high pressure water is re-introduced into the pipes that lead to the sprinklers. The high impact forces experienced by a pop-up rotor type sprinkler are especially prevalent when an empty pipe is being filled with water at a high water pressure. Slugs of water separated by air pockets accelerate down the length of the pipe, and rapidly open the valve in the bottom of the outer case and slam the lower end of the riser to the end of its stroke against a retaining ring positioned at the upper end of the outer case. Due to the high water pressures and large pipe sizes for large turf applications these forces can be extremely high and frequently cause damage to the gear train reduction, reversing mechanism, and other delicate parts of the sprinkler. This often necessitates removal and replacement of the riser. In some cases, the entire sprinkler must be dug out of the ground and replaced. This is especially difficult and inconvenient on a golf course.
Hunter Industries, Inc., the assignee of the subject application, has obtained several patents disclosing sprinkler that are constructed to minimize damage due to rapid extension of the riser. See U.S. Pat. Nos. 5,823,439; 5,823,440 and 5,918,812. See also U.S. patent application Ser. No. 13/445,055 filed Apr. 12, 2012, of Michael L. Clark et al. entitled “POP-UP IRRIGATION SPRINKLER WITH SHOCK ABSORBING RISER DAMPING CUSHION.”
Heretofore the problem of sprinkler damage due to rapid retraction of the riser has not been solved.